Presurgical identification of epileptic foci with iodine-123 iomazenil SPET: comparison with brain perfusion SPET and FDG PET

. Iodine-123 iomazenil (IMZ) has excellent characteristics for the quantification of central benzodiazepine receptor (BZR) binding with single-photon emission tomography (SPET). In order to evaluate the clinical value of IMZ SPET for presurgical identification of epileptic foci in patients with medically intractable seizures, we measured the binding potential (BP) of BZR using two IMZ SPET scans and compared the results with brain perfusion SPET and fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET). A total of ten patients with intractable partial epilepsy were examined by electroencephalography, magnetic resonance imaging, FDG PET, brain perfusion SPET and IMZ SPET. After neuroimaging examinations, five patients underwent selective surgery, and all of them have since been free of seizures. Two SPET scans were performed at 15rmin (early) and 3rh (late) after intravenous injection of ¹²³I-IMZ (167rMBq). Parametric images of the ligand transport (K1) and binding potential (BP) were calculated by the table look-up method, which is based on a three-compartment two-parameter model, using the standard arterial input function obtained by averaging of six normal volunteers’ input functions. BP images delineated the epileptic foci more precisely than either FDG PET or ictal perfusion SPET. FDG PET showed widespread reduction, including the area surrounding the focus, and ictal increase in the cerebral blood flow was seen in possibly activated areas spread from the focus. In four epilepsy cases which originated from the mesial temporal lobe without lateral temporal abnormality, there was no significant decrease in the BP images in the lateral temporal structures, which showed decreased uptake of FDG. It is concluded that parametric images of BP with IMZ are valuable for precise presurgical localization of epileptic foci.     

Limited value of interictal brain perfusion SPECT for detection of epileptic foci: High resolution SPECT studies in comparison with FDG-PET

Accurate localization of epileptic foci is important for pre-surgical evaluation of patients with medically intractable epilepsy, and F-18 FDG PET has been proved to be a valuable method for this purpose. To examine the clinical value with interictal brain perfusion SPECT, we performed brain perfusion SPECT of Tc-99m HMPAO by means of a high resolution SPECT camera, and compared the results with F-18 FDG PET images and MRI in 10 patients with medically intractable epilepsy. In 9 of 10 patients (90%), FDG PET images showed focal hypo-metabolism in the area corresponding with the results of electroencephalography (EEG). SPECT images, however, demonstrated hypo-perfused lesions which corresponded with hypo-metabolic lesions on FDG PET images in only 6 cases (60%). Although MRI showed abnormal findings in 8 cases, the lesions were not directly related to epileptic foci in 2 cases. In conclusion, FDG PET is a valuable tool for accurate localization of epileptic foci. Brain perfusion SPECT, however, may not always be paralleled to metabolism visualized on FDG PET images.     

The utility of a 3-dimensional, large-field-of-view, sodium iodide crystal--based PET scanner in the presurgical evaluation of partial epilepsy.

(18)F-FDG PET is an accurate and reliable technique for localizing medically refractory temporal lobe epilepsy, but widespread use has been hindered by limited reimbursement in many countries because of the high cost of traditional PET equipment and radioisotopes. Additionally, the place of FDG PET as a cost-effective tool for presurgical evaluation of epilepsy has been questioned because of limited data showing that FDG PET provides localization information incremental to that provided by more established techniques, particularly MRI and ictal electroencephalography (EEG). Three-dimensional (3D), large-field-of-view, sodium iodide crystal-based scanners have lower equipment and running costs and better multiplanar resolution than traditional 2-dimensional bismuth germinate (BGO) systems but have not yet been validated for evaluation of epilepsy. Our purpose was to investigate the localization rate, accuracy, and prognostic value of FDG PET images acquired on a 3D, large-field-of-view, sodium iodide crystal-based PET scanner in the presurgical evaluation of intractable partial epilepsy. We also wanted to establish the incremental value of FDG PET over established MRI and ictal EEG techniques. METHODS: Fifty-five patients who were surgical candidates because of medically refractory partial epilepsy were examined. For most of these patients, the lesions had not been clearly localized on conventional assessment. The FDG PET scans were reviewed independently by 2 reviewers who were unaware of the patients' clinical details, ictal EEG findings, and volumetric MRI results, and the FDG PET results were correlated with those of MRI and EEG and with postsurgical outcome. RESULTS: Forty-two patients (76%) had localizing FDG PET images (37 temporal, 5 extratemporal). The ictal EEG recordings were localizing in 66%, and the MRI findings were localizing in 27% (which increased to 35% after the MRI findings were reviewed again after PET). Concordance between the site of the PET localizations and the site of the MRI or EEG localizations was 100%. The PET images were localizing in 63% and 69% of patients with nonlocalizing ictal EEG and MRI findings, respectively. Twenty-one of 24 patients who subsequently underwent epilepsy surgery had localizing FDG PET images; of these 21 patients, 18 (86%) had a class I outcome. Multiple regression analysis showed the FDG PET results to be predictive of postsurgical outcome independently of the MRI findings. CONCLUSION: For intractable partial epilepsy, FDG PET using a 3D, large-field-of-view, sodium iodide crystal-based scanner provided clinically useful localizing information that was at least as accurate as the results reported for traditional BGO-based scanners. The PET images provided prognostically significant localization information incremental to that provided by volumetric MRI and ictal EEG, particularly if 1 of these studies was nonlocalizing.     

The usefulness of repeated ictal SPET for the localization of epileptogenic zones in intractable epilepsy

This study investigated whether repeated ictal single-photon emission tomography (SPET) is helpful in the localization of epileptogenic zones and whether it can provide information confirming that an area of increased perfusion is really the culprit epileptogenic lesion. Fifty-four repeated ictal SPET studies were performed in 24 patients with ambiguous or unexpected findings on the first ictal SPET study. These patients were enrolled from among 502 patients with intractable epilepsy in whom pre-operative localization of epileptogenic zones was attempted with a view to possible surgical resection. Video monitoring of ictal behaviour and EEGs was performed in all patients. Repeated ictal SPET was performed using technetium-99m hexamethylpropylene amine oxime (HMPAO) when there was no prominently hyperperfused area or when unexpected findings were obtained during the first study. Two ictal SPET studies were performed in 19 patients, three studies in four patients and four studies in one patient. The average delay between ictal onset and injection was 28 s for the first study and 22 s for the second, third and fourth studies. Using interictal SPET, ictal-interictal subtraction images were acquired and co-registered with the population magnetic resonance imaging (MRI) template. Invasive study and surgery were performed in 18 patients, and in these cases the surgical outcome was known. In the other six patients, epileptogenic foci were determined using MRI, positron emission tomography (PET) and ictal EEG findings. Two patients were found to have mesial temporal lobe epilepsy, two lateral temporal lobe epilepsy, eight frontal lobe epilepsy, three parietal lobe epilepsy and one occipital lobe epilepsy. The other eight had multifocal epilepsy. The first study was normal in 12 patients (group I) and indicated certain zones to be epileptogenic in the other 12 (group II). Among group I, the correct epileptogenic zone or lateralization was revealed at the repeated study in nine patients, while in the other three it was not. Among group II, six patients showed the same results at the second study, thus confirming that the initially identified zones were of epileptogenic significance. In the other six patients, different areas were identified on the first and second studies, and repeated ictal SPET corroborated multifocality of the ictal EEG findings in five. These results indicate that repeated ictal SPET is useful because it can yield new or additional information about the epileptogenic zones and can confirm that a region of interest is an epileptogenic zone or that the epilepsy is of multifocal origin.     

Is central benzodiazepine receptor imaging useful for the identification of epileptogenic foci in localization-related epilepsies?

In the presurgical evaluation of patients with partial epilepsies, the most extensively studied functional neuro-imaging modality to define the origin of seizure onset is fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET). Generally, this technique reveals a widespread zone of interictal glucose hypometabolism in the region of the epileptogenic focus. However, the technique may miss the epileptogenic region and FDG PET abnormalities may extend beyond the seizure onset zone. Consequently, for the precise identification of epileptogenic regions more specific imaging probes than FDG are warranted. This review considers the clinical utility of iomazenil (IMZ) SPET and flumazenil (FMZ) PET for the precise localization of epileptogenic foci in partial epilepsy syndromes.     

发作期^18F—FDG PET显像对癫痫灶的定位价值

为评价发作期１８Ｆ脱氧葡萄糖（ＦＤＧ）ＰＥＴ显像在癫痫灶定位中的价值，对１５２例癫痫患者进行了发作期１８ＦＦＤＧＰＥＴ检查，并与发作间期图像比较。结果１５２例发作间期示低代谢区患者发作期均呈高代谢，其中６５例（４２８％）为明显高代谢，８７例（５７２％）为相对高代谢。８０例高代谢灶局限于单叶，７２例多发高代谢灶患者中４９例位于相邻近区域。发作期结合发作间期检查，可排除非致痫灶性低代谢病变和癫痫发作过程中痫性活动的播散，提高癫痫灶定位的特异性。     

Ictal postictal and interictal single-photon emission tomography in the lateralization of temporal lobe epilepsy

Single-photon emission tomography (SPET) using radioligands that are fixed on first pass through the cerebral circulation shows distinctive and rapidly changing blood flow patterns accompanying temporal lobe seizures. We sought to determine the optimal time to perform SPET studies for clinical seizure lateralization in temporal lobe epilepsy. Interictal, ictal and postictal SPET scans of 73 consecutively studied patients with unilateral temporal lobe epilepsy were read by three blinded observers to assess the accuracy of lateralization in each condition. The blinded observers correctly identified the side of focus in 97% of ictal studies, 72% of postictal studies and 50% of interictal studies. No incorrect scores were made in the ictal studies, whilst 5% of postictal and 12% of interictal studies were lateralized to the wrong side. Inter-observer agreement was best with the ictal studies. The dramatic perfusion changes of ictal SPET provide consistent, reliable and easily interpretable information that is superior to that provided by interictal and postictal studies. Injection of ligand during seizures is therefore the method of choice for SPET to aid the non-invasive lateralization of temporal seizure foci. Present address: Department of Nuclear Medicine, The Queen Elizabeth Hospital, Woodville, South Australia, Australia     

Application of statistical parametric mapping to SPET in the assessment of intractable childhood epilepsy

Statistical parametric mapping (SPM) quantification and analysis has been successfully applied to functional imaging studies of partial epilepsy syndromes in adults. The present study evaluated whether localisation of the epileptogenic zone (determined by SPM) improves upon visually examined single-photon emission tomography (SPET) imaging in presurgical assessment of children with temporal lobe epilepsy (TLE) and frontal lobe epilepsy (FLE). The patient sample consisted of 24 children (15 males) aged 2.1–17.8 years (9.8±4.3 years; mean±SD) with intractable TLE or FLE. SPET imaging was acquired routinely in presurgical evaluation. All patient images were transformed into the standard stereotactic space of the adult SPM SPET template prior to SPM statistical analysis. Individual patient images were contrasted with an adult control group of 22 healthy adult females. Resultant statistical parametric maps were rendered over the SPM canonical magnetic resonance imaging (MRI). Two corresponding sets of ictal and interictal SPM and SPET images were then generated for each patient. Experienced clinicians independently reviewed the image sets, blinded to clinical details. Concordance of the reports between SPM and SPET images, syndrome classification and MRI abnormality was studied. A fair level of inter-rater reliability (kappa=0.73) was evident for SPM localisation. SPM was concordant with SPET in 71% of all patients, the majority of the discordance being from the FLE group. SPM and SPET localisation were concordant with epilepsy syndrome in 80% of the TLE cases. Concordant localisation to syndrome was worse for both SPM (33%) and SPET (44%) in the FLE group. Data from a small sample of patients with varied focal structural pathologies suggested that SPM performed poorly relative to SPET in these cases. Concordance of SPM and SPET with syndrome was lower in patients younger than 6 years than in those aged 6 years and above. SPM is effective in localising the potential epileptogenic zone but does not provide additional benefit beyond SPET in presurgical assessment of children with intractable epilepsy. The impact of different pathologies on the efficacy of SPM warrants further study.     

Positron emission tomography and single photon emission computed tomography in epilepsy care

Radiopharmaceutical brain imaging is clinically applied in planning resective epilepsy surgery. Cerebral sites of seizure generation-propagation are highly associated with regions of hyperperfusion during seizures, and with glucose hypometabolism interictally. For surgical planning in epilepsy, the functional imaging modalities currently established are ictal single photon emission computed tomography (SPECT) with [(99m)Tc]technetium-hexamethylpropyleneamine oxime (HMPAO) or with [(99m)Tc]technetium-ethylene cysteine dimer (ECD), and interictal positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxyglucose (FDG). Ictal SPECT and interictal FDG PET can be used in presurgical epilepsy evaluations to reliably: (1) determine the side of anterior temporal lobectomy, and in children the area of multilobar resection, without intracranial electroencephalographic recording of seizures; (2) select high-probability sites of intracranial electrode placement for recording ictal onsets; and, (3) determine the prognosis for complete seizure control following anterior temporal lobe resection. Coregistration of a patient's structural (magnetic resonance) and functional images, and statistical comparison of a patient's data with a normal data set, can increase the sensitivity and specificity of these SPECT and PET applications to the presurgical evaluation.     

Reduced GABAA receptor density contralateral to a potentially epileptogenic MRI abnormality in a patient with complex partial seizures

Imaging cerebral GABA_A receptor density (GRD) with single-photon emission tomography (SPET) and iodine-123 iomazenil is highly accurate in lateralizing epileptogenic foci in patients with complex partial seizures of temporal origin. Limited knowledge exists on how iomazenil SPET compares with magnetic resonance imaging (MRI) in this regard. We present a patient with complex partial seizures in whom MRI had identified an arachnoid cyst anterior to the tip of the left temporal lobe. Contralaterally to this structural abnormality, interictal electroencephalography (EEG) performed after sleep deprivation disclosed an intermittent frontotemporal dysrhythmic focus with slow and sharp waves. On iomazenil SPET images GRD was significantly reduced in the right temporal lobe and thus contralaterally to the MRI abnormality, but ipsilaterally to the pathological EEG findings. These data suggest that iomazenil SPET may significantly contribute to the presurgical evaluation of epileptic patients even when MRI identifies potentially epileptogenic structural lesions.     

Benzodiazepine receptors and cerebral blood flow in partial epilepsy.

It was the aim of this study to compare benzodiazepine (Bz) receptor binding and cerebral perfusion in patients with partial epilepsy. Single photon emission tomography (SPET) studies with the flow-marker technetium 99m hexamethylpropylene amine oxine (99mTc-HMPAO) and with the 123I-labelled Bz-receptor ligand Ro 16-0154 (123I-Iomazenil) were performed in 12 patients with partial epilepsy, all with normal magnetic resonance imaging (MRI) and computed tomography (CT) scans. The SPET studies with 123I-Iomazenil were carried out 5 min and 2 h after injection. At 2 h the distribution of activity was very similar to the expected distribution of Bz-receptors in the human brain, known from positron emission tomography (PET) work and post-mortem studies. Early images showed a significantly higher tracer accumulation in the area of the basal ganglia, cerebellum, and naso-pharyngeal space. This finding is caused by non-specific binding and the contribution of the tracer in the blood pool in this phase. Also after 2 h p.i. of 123I-Iomazenil, 9 of the 12 patients showed a focal decrease of of Bz-receptor binding. Ten patients had focal flow abnormalities with 99mTc-HMPAO SPET. In 8 subjects impairment of flow was seen in sites of reduced 123I-Iomazenil uptake. 123I-Iomazenil is suitable for Bz-receptor mapping. In this series of patients, Bz-receptor mapping with SPET seems to offer no advantage over 99mTc-HMPAO in the detection of epileptic foci.     

Brain single-photon emission tomography using technetium-99m bicisate (ECD) in a case of complex partial seizure

The clinical application of technetium-99m bicisate (ethyl cysteinate dimer, ECD) for ictal and interictal studies of regional cerebral blood flow (rCBF) in a patient suffering from medically intractable simple and complex partial seizures is reported. The interictal study was performed 60 min p.i. and the ictal studies were performed at 60 min p.i. using an annular crystal single-photon emission tomography (SPET) system dedicated for high-resolution brain SPET imaging. Visual evaluation of the studies was carried out, as well as semiquantitative measurement of regional tracer uptake. Magnetic resonance imaging (MRI) scans revealed atrophy of almost the complete left frontal lobe and the ventral parts of the left temporal lobe, including in part the temporomesial structures. The left parietal and occipital structures and the right hemisphere were normal. The interictal study showed a large perfusion defect involving the whole left frontal lobe as well as the left temporal lobe with remaining small areas of normal cortical tracer uptake. The ictal studies detected circumscribed hyperperfusion within the left mesial temporal lobe (ventral part of the hippocampus). Additionally an increase in perfusion could be seen within the entire remaining left temporal lobe. Semiquantitative evaluation of tracer uptake comparing both studies detected markedly increased uptake within the focus compared to the remaining left temporal lobe. On this basis the newly available tracer for studies of rCBF, ^99mTc-bicisate, seems to be of value for the detection of epileptogenic foci. Additionally, the value of ictal rCBF studies in the presurgical evaluation of those patients presenting severe morphological alterations on MRI is clearly underlined by this case.     

Pre-surgical identification of epileptogenic areas in temporal lobe epilepsy by 123I-iomazenil SPECT: a comparison with IMP SPECT and FDG PET

OBJECTIVES: The aim of this study was to evaluate the usefulness of (123)I-iomazenil (IMZ) single photon emission computed tomography (SPECT) for the pre-surgical identification of epileptogenic areas in patients with temporal lobe epilepsy and to compare the results with those of (123)I-IMP SPECT and (18)Fluorodeoxyglucose positron emission tomography (FDG PET). METHODS: We examined seven patients with medically refractory temporal lobe epilepsy (five men and two women; mean age, 28 years) with no remarkable findings on magnetic resonance imaging. Before surgery, IMZ SPECT, IMP SPECT and FDG PET were all performed in the interictal state. Then, visual assessment and region-of-interest (ROI) analysis were performed on each image. Final definitions of the epileptogenic areas were made by electrocorticography and histopathology. RESULTS: By IMZ SPECT, a decreased IMZ uptake in the ipsilateral temporal lobe was found in all patients, while a similar decrease in the contralateral temporal lobe was also found in one patient. In comparison to IMP SPECT, the extent of the abnormal area on IMZ SPECT was equal to that on IMP SPECT in one patient while it was more restricted to the epileptogenic area in five patients. In comparison to FDG PET, the extent of the abnormal area on IMZ SPECT was equal to that on FDG PET in three patients while it was more restricted in the epileptogenic area in four patients. In ROI analysis, decreases of IMZ, IMP and FDG uptake were observed in the epileptogenic area, although they were not statistically significant. CONCLUSIONS: IMZ SPECT was considered to be useful for pre-surgical determination of the epileptogenic areas in temporal lobe epilepsy with no remarkable MRI findings, and it was also found to be superior to IMP SPECT and FDG PET for this purpose.     

18F-FDGPET/CT脑显像在癫发作期及发作间期致灶定位中的应用价值

 目的探讨¹⁸F-FDGPET/CT脑3D显像在癫发作期和发作间期致灶定位中的应用价值。方法癫患者60例均行24h头皮脑电图、MRI、¹⁸F-FDGPET/CT脑显像。25例行皮质脑电图(ECoG)或深部脑电图(DEEG)。PET/CT图像经过目测和半定量的方法进行分析。结果(1)60例中,¹⁸F-FDGPET/CT脑显像阳性者57例,检出率95%,其中患者处于发作间期56例,PET/CT表现为低代谢灶者53例,发作期4例,PET/CT上均表现为高代谢灶。(2)PET/CT显示80%为单发灶(48/60),15%为2个以上病灶(9/60)。单发灶中,66.7%位于颞叶(32/48),另33.3%位于颞叶外皮质(顶叶6例,额叶10例)。(3)PET/CT与皮质脑电图(ECoG)或深部脑电图(DEEG)符合率为96%(24/25)。(4)32例颞叶癫行前颞叶切除术,术后随访结果EngelⅠ～Ⅱ级者30例。非颞叶癫16例,行致灶皮质切除术,12例达EngelⅠ～Ⅱ级。3例未检出致灶,9例DEEG定位双侧致灶未行手术治疗。结论对于颅内有病灶癫及明确的颞叶癫患者,PET/CT与EEG以及MRI检查结果具有高度一致性;对于没有病灶及非颞叶癫患者,PET/CT是一种无创、敏感、有效的定位癫源灶的方法。     

46例癫痫患者发作间期~(18)F-FDG PET显像结果分析

目的　探讨18F 脱氧葡萄糖 (FDG)PET对发作间期癫痫灶的诊断价值。方法　 4 6例癫痫患者于发作间期进行CT和 (或 )MRI、头皮EEG及18F FDGPET检查。结果　 4 6例患者中 86 95 %(40例 )PET显像有异常代谢灶 ,其中低代谢灶 3 1例 ,高代谢灶 9例。而CT和 (或 )MRI仅 5 6 5 2 % (2 6例 )异常 ,EEG 82 60 % (3 8例 )异常。 9例示局限性高代谢区患者 1周后在确认检查前后 12h均未发作的前提下再次行PET检查 ,结果发现其中 7例同一部位出现低代谢区 ,另 2例代谢也有所降低。结论　18F FDGPET对发作间期癫痫灶的诊断价值明显优于CT和 (或 )MRI和头皮EEG ,尤其在发作间期和发作期各检查 1次 ,或延长发作后检查时间 ,可提高灵敏度和特异性及诊断准确性。     

Cerebral hypermetabolism demonstrated by FDG PET in familial Creutzfeldt-Jakob disease

Right cerebral and contralateral cerebellar hypermetabolism were observed on FDG PET in a 68-year-old woman with familial Creutzfeldt-Jakob disease (CJD) at an early stage before seizures occurred. The disease progressed with frequent seizures, myoclonus, and a startle reaction. In all past reports, FDG PET studies demonstrated hypometabolism in the cerebrum, cerebellum, and thalamus in patients with CJD. Focal hypermetabolism corresponding with epileptic foci is a common finding in ictal epilepsy patients, and hypometabolism is common in patients with myoclonus or the startle reaction. This finding may reflect a prodromal pathophysiology of epilepsy. Attention should be paid to the diagnosis of CJD while using FDG PET.     

发作间期PET显像与发作期SPECT显像在癫痫灶定位中的应用

目的：探讨发作间期PET显像与发作期SPECT显像在癫痫灶定位中的特点和相关性。方法：对54例癫痫患者行发作间期PET和发作期SPECT2次检查,对结果进行对比分析。结果：54例发作间期PET显像示低代谢者中33例（61．1％）表现为单叶局限性低代谢,21例（38．9％）表现为多个病灶或弥漫性改变。发作期SPECT显像50例可见高灌注灶,高灌注中37例（74％）为单叶局限性高灌注,13例（26％）为多个病灶,未见弥漫性高灌注。2项检查比较,46例（85．2％）2项检查结果相符合,其中32例（69．6％）显示为颞叶病灶。发作间期PET示多病灶及弥漫性改变者于发作期SPECT为像时为9例（42．9％）转化为单叶局限性病灶,7例（33．3％）排除了部分低代谢病灶。结论：癫痫灶灌注与代谢改变具有明显的相关性。发作间期PET显像定位癫痫灶解剖结构显示较为清晰,发作期SPECT显像替代发作期PET检查可提高定位特异。2项检查联合应用可排除非致痫性病变和发作过程中痫性电活动的泛化,具有较好的互补性。     

Benzodiazepine receptors and cerebral blood flow in partial epilepsy

It was the aim of this study to compare benzodiazepine (Bz) receptor binding and cerebral perfusion in patients with partial epilepsy. Single photon emission tomography (SPET) studies with the flow-marker technetium 99m hexamethylpropylene amine oxine (^99mTc-HMPAO) and with the¹²³I-labelled Bz-receptor ligand Ro 16-0154 (¹²³I-Iomazenil) were performed in 12 patients with partial epilepsy, all with normal magnetic resonance imaging (MRI) and computed tomography (CT) scans. The SPET studies with¹²³I-Iomazenil were carried out 5 min and 2 h after injection. At 2 h the distribution of activity was very similar to the expected distribution of Bz-receptors in the human brain, known from positron emission tomography (PET) work and post-mortem studies. Early images showed a significantly higher tracer accumulation in the area of the basal ganglia, cerebellum, and naso-pharyngeal space. This finding is caused by non-specific binding and the contribution of the tracer in the blood pool in this phase. Also after 2 h p.i. of¹²³I-Iomazenil, 9 of the 12 patients showed a focal decrease of of Bz-receptor binding. Ten patients had focal flow abnormalities with^99mTc-HMPAO SPET. In 8 subjects impairment of flow was seen in sites of reduced¹²³I-Iomazenil uptake.¹²³I-Io-mazenil is suitable for Bz-receptor mapping. In this series of patients, Bz-receptor mapping with SPET seems to offer no advantage over^99mTc-HMPAO in the detection of epileptic foci. Offprint requests to: P. Bartenstein     

Neuronuclear assessment of patients with epilepsy

Epilepsy is a common chronic neurological disorder that is controlled with medication in approximately 70% of cases. When partial seizures are recurrent despite the use of antiepileptic drugs, resection of the epileptogenic cortex may be considered. Nuclear medicine plays an important role in the presurgical assessment of patients with refractory epilepsy. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) techniques are used to determine the seizure onset zone, which needs to be resected to render a patient seizure free. Correct localization of the ictal onset zone with the use of SPECT or PET is associated with a better surgical outcome. Ictal perfusion SPECT imaging with (99m)Tc-ethyl cysteinate dimer (ECD) or (99m)Tc-hexamethylpropyleneamine oxime (HMPAO) enables one to detect the seizure onset zone in a majority of cases, especially in patients with temporal lobe epilepsy. Interictal SPECT imaging, which is more widely available, is unreliable to determine the ictal onset zone and is usually only used for comparison with ictal SPECT images. Assessment of the ictal onset zone using subtracted ictal and interictal studies, overlayed on structural imaging has proven to be more sensitive and more specific compared with visual assessment. Video-electroencephalography monitoring in combination with ictal SPECT imaging, however, is only available in specialized centers. It is important to inject the perfusion tracer as early as possible after the beginning of a seizure and to be aware of patterns of seizure propagation. Interictal (18)F-fluorodeoxyglucose (FDG)-PET is routinely used to detect brain areas of hypometabolism, which usually encompass, but tend to be larger than, the seizure onset zone. Also, for assessment of FDG-PET, it is advisable to use an automated technique comparing the patient's images to a normal database in addition to visual interpretation of the images, since automated techniques have proven to be more accurate. In view of the thickness of the cortical ribbon, which may be below the resolution of the PET camera, posthoc partial volume correction or PET reconstruction incorporating the anatomical information of magnetic resonance imaging (MRI), may be useful for optimal assessment of glucose metabolism. Perfusion SPECT and interictal FDG-PET are able to demonstrate areas of abnormal perfusion and metabolism at a distance from the ictal onset zone, which may be associated with cognitive and psychiatric comorbidities, and may represent the functional deficit zone in epilepsy. Part of the functional deficit zone is a dynamic seizure-related process, which may resolve with cessation of seizures. In recent years, novel PET tracers have been developed to visualize not only glucose metabolism but also a wide variety of specific receptor systems. In patients with epilepsy, changes in the gamma-amino-butyric acid(A) receptor, opioid receptor, 5-HT(1A) serotonin receptor, nicotinic acetylcholine receptor systems, and others have been described. Because these tracers are not widely available and the superiority of studying these receptor systems over glucose metabolism in the presurgical evaluation of patients with refractory epilepsy remains to be proven, their use in clinical practice is limited at the moment. Finally, advances in small animal PET scanning allow the in vivo study of the process of epileptogenesis, starting from an initial brain insult to the development of seizures, in animal models of epilepsy. Potential new therapeutic targets may be discovered using this translational approach.     

HIPDM-SPECT brain imaging in the presurgical evaluation of patients with intractable seizures

We report the results of interictal and ictal HIPDM-SPECT brain imaging in 34 patients who eventually underwent temporal lobectomy for treatment of medically intractable complex partial seizures. Interictal studies revealed decreased regional cerebral perfusion (rCP) in the temporal lobe corresponding to the eventual site of surgery in 73% of the patients. Similarly, ictal study demonstrated increased rCP in 93% of the patients. In 69% of the patients, the SPECT studies were able to demonstrate both increased rCP on the ictal scan and decreased rCP on the interictal scan in the same location, corresponding to the eventual site of surgery. These results suggest that interictal and ictal SPECT brain imaging can be easily obtained and provide reliable localizing information in the presurgical evaluation of patients with medically intractable epilepsy.